Multifilament glass fiber strands or cords are known to have advantageous characteristics for reinforcing elastomeric products such as pneumatic tires, hoses, belts, etc. However, it has been found that these advantageous characteristics can only be practically realized when the strands or cords have been impregnated with a suitable polymeric or resinous material (impregnant) which largely fills the interstices between the individual filaments in each strand or cord and also largely coats the outer surface of the strand or cord. When so disposed, a suitable impregnant appears to bind the individual filaments of each cord together into an integral unit, to provide adhesion of the cord to the elastomeric matrix in which it (or fabric woven therefrom) is embedded as reinforcement, and also to furnish a cushioning medium flexibly separating the individual filaments in each strand or cord from one another so as to permit at least a modest amount of relative motion between such filaments during normal deformations of the elastomeric products reinforced with such impregnated cord while minimizing mutual abrasion of the filaments during such relative motion. Ordinarily, and preferably, the individual glass fibers will have been very lightly coated immediately upon formation with a suitable sizing composition comprising a film-forming resin or polymer, a lubricant and a coupling agent in order to protect them from abrasion during subsequent handling and to enhance the adhesion of the impregnant to the individual filaments.
The most satisfactory impregnating compositions heretofore known for glass fiber cords to be used in the reinforcing belts for radial pneumatic tires have been aqueous compositions comprising polybutadiene homopolymer latex, butadiene-styrene-vinylpyridine terpolymer latex, a resorcinol-formaldehyde resin, a wax emulsion, a thickening agent containing polymerized methacrylic acid and a defoaming agent comprising a suitable blend of emulsifiable mineral oils, silica derivatives and esters. Such impregnating compositions and the impregnated cords produced therewith are described in U.S. Pat. Nos. 4,060,658 entitled Glass Fibers Coated With A Polybutadiene Homopolymer Latex-Containing Impregnant, issued to Lin and Hammond on Nov. 29, 1977, and 4,107,117 entitled Tire Cord Impregnant, issued to Lin and Hammond on Aug. 15, 1978, both of which are incorporated herein by reference. Since it was not previously recognized that the nature of the emulsifying surfactant used for the polymer latex components of these impregnating compositions had any significant effect on the properties of the impregnated cord, the nature of those surfactants was not indicated in these two patents, but in fact anionic rosinate surfactants have heretofore been employed for emulsifying the polybutadiene homopolymers and the butadiene-styrene-vinylpyridine terpolymers of such impregnating compositions.